If Evolution is a slow change, or adaptation of a given species over time, in response to enviromental demands, then evolution is a fact. Maybe you are having issues with your concept of what evolution is? Many JW's do not have the foggiest notion of what evolution is, therefore they dismiss it off-hand. What they really have an issue with is the origin of life itself. The JW concept of Satanic evolution is disrespectful to the creator, they feel.
When you are raised believing that you have " the truth ", you no longer search for answers. Why should you? JW "scholars" believe that they are educated because they read the Awake, and fact check with the WT CD-Library and JW.org, and the Appendix of the NWT.
From a biblical point of view, not much is said about the creation process of animals and plants. The most details given concern man, and there isn't much information. We are told that GOD formed man from the elements of the earth, that's about it. With so many details omitted, it's a little silly to claim that we KNOW how this was done. Even scientists do not KNOW how everything really came about. They just KNOW what they observe and test. That is one of the limitations of the scientific method. Still, animals do change over time to survive, that is a fact. It is verifiable, therefore it is truth.
It's disconcerting when our "truths" meet facts. It can be the beginning of a journey that many are reluctant to take. It can also trigger such fear, that anyone discussing facts, instead of " truths ", may find themselves subject to an inquisition and subsequent excommunication.
Watch the StarTrek " Distant Origin" episode. It's really cool.
Peace,
DD